SpA Detection Varies Widely Among Countries

Spondyloarthritis most likely underdiagnosed, authors says

Action Points

Spondyloarthritis and its subtypes may be underdiagnosed, and improved diagnosis will likely translate to increased prevalence.

Note that ankylosing spondylitis was more prevalent in samples with a lower percentage of females, and in studies from North America, Europe, and the Northern Arctic, as well as in samples from rural versus urban areas.

Spondyloathritis (SpA) and its subtypes may be underdiagnosed, and improved diagnosis will likely translate to increased prevalence, according to a Dutch meta-analysis.

In a review of literature published from 1975 to 2014, pooled SpA prevalence, reported in 30 studies, ranged widely across the world, from 0.20% (95% CI 0-0.66) in Southeast Asia to 1.61% (95% CI 1.27-2) in the Northern Arctic, reported Carmen Stolwijk, MD, PhD, of Maastricht University Medical Center in The Netherlands, and colleagues.

This study is the first to pool global estimated prevalences of SpA and its subtypes in the general population and to investigate demographic and methodologic characteristics influencing them, the authors wrote in Arthritis Care & Research.

Noting that SpA is probably underreported, the authors said "high quality studies are needed to estimate the prevalence of axial and peripheral SpA in the general population, and to estimate the prevalence of SpA in developing countries."

A single, bias-prone study found a higher SpA prevalence in North America of 1.35% (95% CI 0.44-2.79), and in Europe of 0.54% (95% CI 0.36-0.78), compared with South Asia's 0.22% (95% CI 0.01-0.66) and Southeast Asia's 0.20%. No studies were available from Sub-Saharan Africa, Central Asia, or Oceania.

Overall, heterogeneity in the prevalence of SpA was strongly associated with demographic and methodologic factors such as a lower proportion of females, the mean age of the sample, geographic area, setting (urban/rural/combined), case finding, case ascertainment, and year of data collection. Prevalence rose with data collected in the years 2000 and later, suggesting heightened disease awareness and recognition, and also rose in smaller studies with samples fewer than 5,000.

Ankylosing spondylitis (AS, reported in 53 studies) varied in prevalence from a low of 0.02% (95% 0-0.21) in Sub-Saharan Africa to a high of 0.35% (95% CI 0.24-0.48) in Northern Arctic communities. The prevalence of psoriatic arthritis (35 studies) extended from 0.01% (95% CI 0-0.17) in the Middle East to 0.19% (95% CI 0.16-0.32) in Europe.

AS was more prevalent in samples with a lower percentage of females (P<0.01), and in studies from North America, Europe, and the Northern Arctic, as well as in samples from rural versus urban areas (P<0.01). The proportion was lower in samples in which cases were found by medical records compared with two-step symptom approaches (P<0.01), but higher in studies with a high risk of bias for the validity of the study instrument (P<0.01).

Geographic area and case findings emerged as the most significant drivers of variation. The effect of geographic region might relate to genetic characteristics such as a higher proportion of SpA-related HLA-B27 positivity, according to the authors.

"Independent of other characteristics, the highest prevalence estimates of SpA were found in Northern Arctic indigenous communities, in which up to 50% of people have been reported to be HLA-B27 positive," Stolwijk's group wrote.

Too few studies were available to conduct meta-analyses on the other SpA subtypes, but prevalence estimates of reactive arthritis (range 0.0%-0.2%), SpA related to inflammatory bowel disease (range 0.0%-0.1%), and undifferentiated SpA (range 0.0%-0.7%) were generally low.

Specifically, the prevalence of reactive arthritis ranged from 0.03% in Greece to 0.21% in Lithuania, while a hospital-based study from Zimbabwe reported a prevalence of 0.001%. Northern Arctic indigenous communities had a prevalence range of 0.25% to 1%.

Spondyloarthritis associated with inflammatory bowel disease (IBD-SpA), reported only in European studies, ranged from 0% in Greece to 0.09% in Italy. However, there are no formal criteria to classify IBD-SpA, the authors cautioned.

As for undifferentiated SpA, most European studies reported prevalences of 0.03% to 0.10%. A Turkish study found a prevalence of 0.56%, and a German study a prevalence of 0.67%. In two Asian studies, the reported prevalences were 0.15% in India and 0.55% in China. In Northern Arctic indigenous people, prevalence ranged from 0.20% to 1.3%.

The study had limitations, including a potential language bias owing to the inclusion of articles written only in English, French German, Dutch, Spanish, or Italian. Also, prevalence could vary within the defined geographic regions. A high risk of bias was noted for the "representativeness" of the samples, and since not all analyses were true general population studies, generalizability was problematic. An additional limitation was that most studies did not address the prevalence of HLA-B27.

Moreover, the diagnosis of spondyloarthritis is challenging, according to Nortin Hadler, MD, of the University of North Carolina at Chapel Hill, in the absence of disease definition by “full-blown, classic pathology on imaging studies,” which is the only route to reliable prevalence estimates of these rare conditions.

“The real challenge for clinicians and epidemiologists alike is to identify earlier and forme fruste disease,” he noted.

“Few clinicians shy away from this challenge with the result that this disease category in large data sets reflects the eyes of the beholder more than the plight of the afflicted,” Hadler told MedPage Today.

Stolwijki and co-authors disclosed no relevant relationships with industry.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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